Method for mounting a bush around a part of a shaft by means of a tight fitting

ABSTRACT

Method for mounting a bush round a part ( 2 ) of a shaft with a force fit, which method comprises the following steps: providing a guide element ( 7, 23 ) with an outer surface ( 8 ) which is at least partly conical; providing the guide element ( 7, 23 ) in the extension of the aforesaid part ( 2 ) of the shaft ( 1 ); pushing the bush ( 5 ) over the guide element ( 7, 23 ) on the part ( 2 ) of the shaft ( 1 ).

The present invention concerns a method for mounting a bush on a part ofa shaft with a force fit.

Without limiting the invention thereto, the field of application of theinvention may be for example mounting a bush round a rotor shaft withpermanent magnets of an electric machine, or any application whatsoeverwhereby a bush must be fixed in a non-rotating manner on a part of ashaft and whereby the bush is subject to turning forces, as is forexample typically the case with applications having high rotationalspeeds.

Methods for fixing an element on a cylindrical part of a shaft arealready known.

In many cases, as described for example in U.S. Pat. No. 4,549,341, anelement with an inner passage whose inner diameter is smaller than theouter diameter of the aforesaid part of the shaft is taken.

In order to be able to apply such a type of element over the cylindricalpart of the shaft, these known methods make use of the principle thatobjects expand when being heated and shrink when being cooled.

By heating the element and cooling the aforesaid part of the shaft, thedifference between the inner diameter of the element and the outerdiameter of the shaft is hereby eliminated, such that the element can bepushed over the cylindrical part of the shaft, after which, as theelement is cooled down and the shaft is heated again, a shrink fit canbe obtained.

A first disadvantage of these known methods is that they can only beapplied with materials having a sufficiently high thermal expansioncoefficient.

Another disadvantage of this known method is that the element must bestrongly heated to obtain a sufficient expansion, which may cause damageto the element or even to the shaft.

With elements in the shape of permanent magnets, said heating may changethe magnetism of the magnets.

Also with elements made of a polymer or plastic, such a heating may befatal, as a result of which the field of application of this knownmethod is restricted.

Further, heating large elements in a consistent manner, for examplemetal rings or the like, is very expensive and not simple.

Moreover, there is a danger with said known method in that, whenapplying the heated element on the shaft, the element will cool down toofast and will get stuck on the shaft before it has been put in the rightplace, with all the ensuing consequences.

With other known methods for applying an element on a shaft, as knownfor example from U.S. Pat. No. 5,188,478 and U.S. Pat. No. 6,104,115,the part of the shaft is provided with a conical outer surface on whichhas been provided an element with a complementary conical passage.

A disadvantage of such conical embodiments is that they are expensive.

Even if the element is made of a fibre-reinforced composite, forexample, it will be hard to produce large numbers due to the conicalshape of the element.

For, when manufacturing for example a conical composite ring, the innerconicity of the ring will be obtained by winding a strip of compositearound a conical mandrel which is restricted to the length of one ringbecause of the required conicity.

On the contrary, it is easy to cut a cylindrical composite ring from amuch longer cylindrical tube, whereby such a cylindrical tube can beobtained by winding a strip of composite around a cylindrical mandrelwhose length may be chosen at random.

As a result, it is intrinsically much easier to produce cylindricalrings than conical rings.

Therefore, the present invention aims to remedy one or several of theaforesaid and/or other disadvantages.

In particular, the invention aims to obtain a cost-effective method formounting a bush on a part of a shaft with a force fit.

The aim hereby is to obtain a force fit between the bush and the shaft,without a complicated shape being required for the bush to this end,such as for example a conical surface, a conical passage or the like.

Another aim of the invention is to obtain a method which can be appliedat room temperature and whereby the bush is made for example of asynthetic material, such as a fibre-reinforced composite, or of a metalor the like.

To this end, the present invention concerns a method for mounting a bushon a part of a shaft with a force fit, which method comprises thefollowing steps:

-   -   providing a guide element in the extension of the aforesaid part        of the shaft, whereby this guide element has an outer surface        which is at least partly conical and whose largest diameter        deviates maximally five percent from the outer diameter of the        aforesaid part of the shaft and whereby the guide element is        positioned such that the largest diameter of the conical part is        directed to the aforesaid part of the shaft;    -   pushing the bush over the guide element on the side of the guide        element with the smallest diameter and on the aforesaid part of        the shaft;    -   moving a press axially towards the conical part during a first        step in shifting the bush over the guide element, whereby this        press is provided with a bearing face on which the entire end        face of the bush can rest during the pressing; and,    -   making use of a press element with an inner diameter which is        equal to or larger than the outer diameter of the part of the        shaft during another step in shifting the bush over the guide        element.

An advantage of such a method according to the invention is that thebush must not be provided with a complex shape which is difficult torealise, such as for example a conical surface, in order to obtain asolid connection between the shaft and the bush.

Another advantage of a method according to the invention is that it canbe applied at room temperature.

In this way, there is no risk of damaging the shaft or the bush by meansof surface oxidation or the like resulting from heating in order toshrink-fit the bush on the shaft, as is the case with some knownmethods.

Moreover, with such a method according to the invention, whereby noheating is required, the bush can be made of a composite, for example aglass fibre-reinforced composite, whereby the fibres preferably extendin all directions in relation to one another.

Another advantage of such a method according to the invention is thatbushes having a longer length can be clamped on a shaft than is possiblewith the known methods.

Indeed, by making the press rest with a bearing face on the entire endface of the bush during the pressing in a first step to push the bushover the guide element, the risk that the bush will bend under thepressure force is strongly reduced.

Moreover, the axial strength of the bush is maximally used.

As a result, a larger frictional force between the bush and the guideelement or the shaft can be overcome while pushing than with the knownmethods.

Since this frictional force is proportional to the contact surfacebetween the aforesaid parts and thus increases as the length of the bushincreases, bushes with a larger length can consequently be pushed over ashaft or guide element with a method according to the invention.

This offers the additional advantage that much time can be gained duringthe assembly.

Indeed, a method according to the invention requires less operations toclamp a bush with a relatively large length on the shaft than when ashaft with the same length must be provided with a bush by applying theknown methods, whereby several bushes must be necessarily clamped oneafter the other on the shaft in this case.

Also, with a method according to the invention, the risk for other failmodes of the bush to occur while pressing is smaller, especially withbushes made of a composite.

By applying an inappropriate press method, the constituent parts of acomposite bush might delaminate, for example, or cracks might occur forexample in the outer composite layer or layers and the like.

Said risk is restricted to a minimum with a method according to theinvention.

According to a preferred method of the invention, during the aforesaidfirst step to axially shift the bush over the guide element, the pressis axially moved up to the conical part of the guide element.

Thus, the press will rest on the entire end face of the bush as long asthis is possible during the first shifting step, which is of courseadvantageous to the stability of the bush while pressing.

According to a preferred method of the invention, the shaft is steppedand the guide element is at least partly hollow, whereby the guideelement is centred on the shaft by providing it with its hollow partover a part of the shaft having a smaller diameter than the aforesaidpart of the shaft over which the bush must be provided.

Such centring of the guide element on the shaft is very simple andpractical.

According to an alternative method of the invention, the shaft isprovided with a recess on its far end, and the guide element is providedwith an axially protruding part which is complementary to the recess inthe shaft, whereby the guide element is centred on the shaft by placingit at least partly in the recess of the shaft with its axiallyprotruding part.

Such a method may be practical for example when the bush must beprovided at the far end of the shaft or close to the far end of theshaft.

In order to better explain the characteristics of the invention, thefollowing preferred embodiments of a method according to the inventionfor mounting a bush on a part of a shaft with a force fit are describedby way of example only without being limitative in any way, withreference to the accompanying drawings, whereby FIGS. 1 to 10 includedillustrate the successive steps of the method seen as a section, and inwhich:

FIG. 1 is a side view of a part of a stepped shaft;

FIG. 2 shows how a guide element is provided over the stepped shaftaccording to FIG. 1;

FIG. 3 illustrates how a bush is provided over the guide element;

FIG. 4 shows how a press can be placed up against the bush;

FIG. 5 shows the condition after the press has been moved axially upagainst the conical part of the guide element;

FIG. 6 shows the condition after the press has been removed;

FIG. 7 illustrates how an additional accessory is placed against thebush;

FIG. 8 shows how the press can be applied up against the additionalaccessory again;

FIG. 9 shows a condition whereby the bush has been moved axially up to apart of a shaft by means of the additional accessory and the press;

FIG. 10 shows the clamped joint that is eventually obtained between thebush and the part of a shaft;

FIG. 11 shows an alternative embodiment analogous to FIG. 9 whereby yetanother additional accessory is used as an intermediate step;

FIG. 12 shows an alternative embodiment whereby the shaft is providedwith a cavity on its far end in which the guide element is introduced ina fitting manner; and,

FIGS. 13 to 17 included illustrate frequently occuring failure modeswhen applying the known methods for mounting a composite bush on a partof a shaft with a force fit, which are avoided with a method accordingto the invention or at least occur less frequently.

The invention concerns a method for mounting a bush on a part of a shaftwith a force fit.

FIG. 1 represents a section of one far end of a stepped cylindricalshaft 1, with in this case at least three cylindrical parts 2, 3 and 4of the shaft 1, summed up here according to a decreasing shaftthickness, whereby every part 2 to 4 of the shaft 1 has its owndiameter, being the respective diameters D1, D2 and D3 from large tosmall.

Such a shaft 1 is merely an example of a shaft to which the methodaccording to the invention relates and it could be for example a rotorshaft of an electric generator, whereby permanent magnets are providedin the rotor shaft and whereby over the shaft 1 must be provided a bushto protect the magnets for example.

In another application, the shaft 1 could be for example the shaft of acombustion engine, around which is provided a flywheel to make the motorshaft run more steadily.

Of course, many other applications are not excluded either.

In what follows, for simplicity's sake, it is assumed, however, that thebush 5, represented in FIGS. 3 to 12 included, must be provided with aforce fit on the cylindrical part 2 of the shaft 1.

The bush 5 has a cylindrical passage 6 with an inner diameter D4 whichis smaller than the outer diameter D1 of the part 2 of the shaft 1 onwhich the bush 5 must be fixed.

The method according to the invention comprises the step of providing aguide element 7 with an outer surface 8 which is at least partlyconical.

On the one hand, the largest outer diameter D5 of the conical part 9 ofthe guide element 7 hereby deviates maximally five percent from theouter diameter D1 of the part 2 of a shaft 1 on which the bush 5 must befixed.

On the other hand, the smallest outer diameter D6 of the conical part 9is in this case smaller than, or possibly in other cases, maximallyequal to the inner diameter of the bush 5.

Preferably, at least the guide element 7 of the bush 5 is provided witha rounding on the edge of the contact surface between both, whereby theradius of the aforesaid rounding is preferably situated within a rangeof 10⁻¹⁰ times the smallest diameter D6 of the conical part 9 to 10⁻¹times the smallest diameter D6 of the conical part 9. The edges referredto are respectively represented in FIG. 3 by the references R and R′.

In the example discussed here, the outer surface 8 of the guide element7 is also provided, on the side 10 of the conical part 9 with thesmallest diameter D6, with a cylindrical part 11 which connects to theconical part 9 via a collar transition.

The outer diameter D7 of said cylindrical part 11 is in this casesmaller than the smallest diameter D6 of the conical part 9.

According to the invention, said diameter D7 may in other cases bemaximally equal to the diameter D6, in which latter case the cylindricalpart 11 is connected directly to the conical part 9 without any collartransition.

Further, in the example of FIGS. 1 to 11 included as discussed here, theguide element 7 is made at least partly hollow.

More specifically, the guide element 7 is in this case provided with acentral passage 12 with an inner diameter D8 which corresponds to thediameter D2 of the shaft part 3 adjacent to the part 2 of the shaft 1 onwhich the bush 5 must be fixed.

Consequently, the guide element 7 can be centred on the shaft 1, such asis illustrated for example in FIG. 2, by providing it with its hollowpart or its passage 12 over the part 3 of the shaft 1 having a smallerdiameter D2 than the part 2 of the shaft 1 over which the bush 5 must beprovided.

According to a method of the invention, the aim hereby is to place theguide element 7, more particularly the conical part 9 of the guideelement 7, in the extension of the part 2 of the shaft 1, whereby morespecifically the conical part 9 of the guide element 7 with the largestouter diameter D5 is directed to the part 2 of the shaft 1.

As is illustrated in FIG. 3, the bush 5 with its passage 6 can besubsequently placed over the provided guide element 7 on the other sideof said guide element 7.

Next, a force F is exerted on the bush 5 in the axial direction AA′ anddirected towards the part 2 of the shaft 1 so as to slide the bush 5over the guide element 7 on the part 2 of the shaft 1. Finally, theguide element 7 is removed again in this case.

The axial force F can be exerted in many ways, whereby the method cancomprise two or several steps, for example as a function of thethickness h of the wall of the bush 5 or as a function of the auxiliarymeans used when exerting the axial force F.

A preferred way of exerting the axial force F on the bush 5 consists inusing a cylindrical press 13 which is for example partly hollow or, asrepresented in the given example of FIG. 4, entirely hollow.

The press 13 is in this case more specifically provided with a centralrecess 14 having an inner diameter D9 which corresponds practically tothe outer diameter D7 of the cylindrical part 11 of the guide element 7.

The aim of the method according to the invention hereby is to exert anaxial force F on the bush 5 with the press 13, such that the bush 5slides over the conical part 9 of the guide element 7, whereby the press13 itself is moved over the cylindrical part 11 of the guide element 7during said axial movement.

The hollow press 13 is provided with an overhang 15 which serves as abearing face against which the entire end face 16 of the ring 5 can restin a first step during the pressing.

This reduces the risk for the ring 5 to be upset or to buckle inwardduring the pressing.

Moreover, according to a method of the invention, during this first stepto slide the bush 5 over the guide element 7, the cylindrical press 13is preferably moved axially up to the conical part 9 of the guideelement 7.

This is illustrated in FIG. 5.

In the given example, the press 13 cannot even be moved further to thepart 2 of the shaft 1, since the diameter D9 of the recess 14 in thepress corresponds over the entire length of the press 13 to the outerdiameter D7 of the cylindrical part 11 of the guide element 7, wherebythe difference between the diameters D6 and D7 moreover forms a sort ofstop.

This can be avoided for example by providing a part of the recess 14 inthe press 13 with a somewhat larger diameter.

However, as a consequence, the contact surface between the press 13 andthe end face 16 of the bush 5 is reduced as well, which could contributeto the bush 5 being upset or being buckled inward.

In order to avoid this, an extra support may possibly be provided forwhile the bush 5 is being pressed over the conical part 11, for exampleby selecting equal or practically equal diameters D4, D6 and D7.

After the removal of the press 13, a situation is obtained as isrepresented in FIG. 6.

In order to be able to slide the bush 5 even further over the conicalpart 9 of the guide element in the axial direction AA′ towards the part2 of the shaft 1, according to a special aspect of the invention, use ismade of an additional accessory 17 in a following step of the method.

As is represented in FIG. 7, such an accessory 17 may consist forexample of a cylindrical press element 17 having a stepped recess 18.

In the given example, the recess 18 is realised with an inner diameterD10 for a part 19 which is larger than the inner diameter D4 of the bush5 or than the smallest diameter D6 of the conical part 11 of the guideelement 7.

More specifically, said diameter D10 of the aforesaid part is in thiscase equal to or somewhat larger than the outer diameter D1 of the part2 of the shaft 1.

Further, the recess 18 of the adjacent part 20 of the accessory 17 hasan inner diameter D11 which corresponds to the diameter of thecylindrical part 11 of the guide element 7.

As a result, it is possible to centre the accessory 17 with the recess18 of the part 20 on the guide element 7, while the accessory 17 canrest against the bush 5 with its far end 21 at the part 19, and the bush5 can slide partly or entirely over the conical part 9 of the guideelement in the axial direction AA′, when an axial force F is beingexerted on the accessory 17.

As shown by means of FIG. 8, such an axial force F can be exerted on theaccessory 17 by means of the press 13 after it has been provided in acentred manner on the guide element 7 again by pushing the press 13 overthe cylindrical part 11 of said guide element 7 again until it restswith its overhang 15 up against the accessory 17.

As shown in FIG. 9, when exerting an axial force F on the accessory 17,the bush 5 can shift over the conical part 9 of the guide element 7,whereby, in the given example, the maximal length over which sliding inthe axial direction is possible in this step, is determined by thelength of the part 19 of the accessory 17 with the wider passage D10.

It should be noted that the diameter D10 in this case is alsosufficiently large to press the bush 5 up to the part 2 of the shaft 1.

After removal of the press 13, the accessory 17 and the guide element 7,the situation as represented in FIG. 10 is obtained, whereby a bush 5 ismounted on the part 2 of the shaft 1 with a force fit, without thethermal expansion qualities of the used material having been used duringthe mounting to that end.

Sometimes, it may be useful to apply several analogous intermediatesteps, whereby several successive alternative accessories 22 are appliedwhen axially the bush 5 over the guide element 7, whereby in everysubsequent step an alternative accessory 22 with an ever increasinginner diameter D10 is used.

The use of such an accessory 22 is illustrated by means of FIG. 11.

It is clear that, when the thickness h of the wall of the bush 5decreases and the difference between the inner diameter D4 of the bush 5and the outer diameter D1 of the part 2 of the shaft 1 on which the bush5 is to be fixed increases, several such intermediate steps willpreferably have to be used.

Indeed, the last accessory 17 which is applied according to the methodmust always have an inner diameter D10 which is at least as large as thediameter D1 of the part 2 of the shaft 1.

If the bush 5 has a thin wall and the difference in diameter D1-D4 tospan is large, such an accessory 17 or 22 will only rest on a veryrestricted part of the end face 16 of the bush 5 during the pressing,which might cause buckle problems or the like.

In extremis, if a bush 5 were to be used having a thickness h which, issmaller than the difference in diameter D1-D4 to span, it would beimpossible to obtain any deformation of the bush 5 by means of a singleaccessory 17.

Such a case might occur in practice if a material were to be used whichis very elastic in a radial direction, but relatively rigid in the axialdirection.

Indeed, the required large radial expansion of the bush 5 requires alarge elasticity of the bush 5, whereas when pressing according to amethod of the invention, a non-negligible axial force F must be exertedon the bush 5.

Such a material could be for example a fibre-reinforced composite whosefibres are directed such that a good radial elasticity and a large axialstrength are obtained. A large radial elasticity is actually a qualityof modern composites.

For that matter, one of the merits of the present invention is that itmakes it possible to shift a thin-walled bush 5 having a thickness h andan original inner diameter D4 over the shaft 1 with an outer diameterD1, whereby the difference in diameter D1-D4 is larger than thethickness h of the bush 5.

This is not possible with the known techniques.

The following dissertation hereby illustrates what advantage this mayoffer.

For, the purpose is for the bush 5 to exert a certain radial pressure Pon the shaft 1 after having been clamped on it so as to be able toresist the rotor forces.

This radial pressure P is represented by the following formula:

P=(h.σ)/D4=(h.ε.E)/D4

whereby

-   -   P is the pressure exerted on the shaft 1 by the bush 5;    -   h is the thickness of the bush 5;    -   D4 is the inner diameter of the bush 5;    -   E is the Young modulus of the material out of which the bush 5        is made;    -   σ is the radial tension in the bush 5; and,    -   ε is the radial deformation of the bush 5.

It is clear that, in order to obtain the same radial pressure P on theshaft 1, one may opt for a bush 5 having a relatively large thickness hwhich is only subject to a small deformation ε, as well as for a bush 5having a relatively small thickness h which is subject to a largerdeformation ε.

The latter option is more economical in many cases, since one can saveon the material of the bush 5 itself.

However, with the known methods whereby only one step is used during thepressing, only a limited deformation of the bush 5 can be obtained.

By applying a method according to the invention with two or severalsteps during the pressing, a much larger deformation of the bush 5 canbe obtained, and thus a smaller thickness h of the bush 5 can beselected.

Moreover, it is known that in magnetic circuits whereby the magneticfield passes through an air gap, such as for example in the case ofmotors with permanent magnets, the air gap between rotor and stator ispreferably restricted as much as possible so as to restrict the magneticresistance or reluctance.

By applying a method according to the invention, it is possible forexample to embed such permanent magnets in a rotor and to screen themwith a bush 5 having a thickness h which can be selected much smallerthan with the known methods, since a larger radial extension can beobtained with a method according to the invention.

As a result, also much less magnetic material will be required, whichagain implies a big cost saving.

Further, according to the invention, the apical angle α of the conicalpart 9 of the guide element 7 is preferably not too large, preferablybetween 0.01° and 15°, since with a small apical angle α, by exerting anaxial force F, the bush 5 can be deformed relatively more easily thanwith a larger angle α.

Preferably even, this apical angle α is selected smaller than or equalto the value obtained according to the following formula:

α=k.|ε|.D4/(h.(D1-D4))

whereby:

-   -   α=the maximal apical angle in °;    -   k=a factor which is selected on the basis of the way in which        the bush 5 is composed and the material out of which the bush 5        is made, which factor is situated within a range of 10⁻⁶ to        10⁻²;    -   |ε|=the absolute value of the maximally possible elongation for        the least elastic material component of the bush 5 or the        plasticity limit of the metal, provided the bush is made of        metal;    -   h=the thickness of the wall of the bush 5 in m;    -   D4=the inner diameter of the bush 5 in m; and,    -   D1=the outer diameter of the part 2 of the shaft 1 in m.

By taking into account this calculation method, the axial force F iskept within bounds, as a result of which certain manners of failure ofthe bush 5 during the pressing can be avoided, as will be furtherexplained.

According to a non illustrated variant, use can be made of a guideelement which comprises a number of successive conical parts over itslongitudinal direction, whereby every conical part meets the aforesaidformula and whereby D1 is each time determined by the largest outerdiameter of the conical part concerned.

By selecting an apical angle α which is sufficiently small, problems canbe avoided such as for example delamination of the layers (FIG. 15) outof which the bush 5 is made or cracking of the composite on the outsideof the bush 5, as is illustrated by means of FIG. 16.

Moreover, the smaller the apical angle α is selected, the easier thedeformation of the bush 5 over the conical part 9 of the guide element 7can be obtained.

A k value which is practically equal to 10⁻⁴ is thought to beappropriate according to the invention, for example to avoid theaforesaid effects, whereby with this k value a wide range of materialsused for the bush 5 and of manners to compose the bush 5 is covered.

Preferably, the bush 5 is made of a plastic, and most preferably even ofa composite which is for example fibre-reinforced.

According to a special characteristic of the invention, the bush 5 ismade of different layers of composite which are either or notfibre-reinforced, whereby the layers which are situated near the outerperimeter of the bush 5 have a larger elasticity than the layers whichare situated near the inner wall of the above-mentioned bush 5.

Such a composite bush is preferably made of a fibre-reinforced compositewith at least one of the following layers or a combination thereof:

-   -   an inner layer whose fibres are wound in a direction extending        between +/−70° and 90° in relation to the shaft of the bush (5);    -   an intermediate layer whose fibres are wound in a direction        extending according to a direction between +/−70° and 90° in        relation to the shaft of the bush (5);    -   an axial layer whose fibres are wound in a direction extending        according to a direction between 0 and +/−70° in relation to the        shaft of the bush (5); and,    -   an outer layer whose fibres are wound according to a direction        extending between +/−70° and 90° in relation to the shaft of the        bush (5).

The different angles for the fibre directions can hereby be adjusted asa function of the required strength for the bush 5.

According to another preferred method of the invention, the aforesaidinner layer of such a composite bush 5 is made with carbon fibre.

The method according to the invention is very appropriate for clampingbushes 5 on a shaft 1, and especially for pressing composite bushes 5 ona shaft 1.

Indeed, with a method according to the invention, a number of failuremodes are avoided which may occur when pressing bushes 5 over a cone 9,a number of failing manners of which will be discussed hereafter bymeans of FIGS. 13 to 17 included.

By first of all making use of a press 13 with a method according to theinvention which rests on the entire end face 16 of the bush 5, or of anaccessory 17 which rests on the entire end face 16 of the bush 5, therisk for the bush 5 to buckle is very much reduced or entirelyeliminated.

If this were not the case, the bush will easily buckle inward, as shownin FIG. 13, since during this first pressing phase, the far end of thebush 5 at the press 13 or at the accessory 17 is not internallysupported.

Moreover, the asymmetrical force of the press 13 or the accessory 17acting on the bush 5, as well as the orientation of the cone 9 furtherpromote the buckling.

Another failing mode which may occur with bushes 5 made of severallayers, such as for example made of a composite, consists in that thelayers delaminate during the pressing.

Such failure modes are illustrated by way of example in FIGS. 14 and 15,whereby the layers delaminate on the far end of the bush 5 near thepress 13 or the accessory 17 and on the far end of the bush 5 which hasalready been pushed over the shaft part 2 respectively.

The reason why the layers of the bush 5 come off is mainly that a toolarge apical angle α is taken for the cone part 9 of the guide element7.

FIG. 16 shows yet another failure mode of the bush 5 which may occur dueto an inappropriate selection of the apical angle α for the cone part 9.

In particular, a too large apical angle α and a too small roundingbetween the cone part 9 and the shaft part 2 cause a change in directionin the bush 5 which is too abrupt, as a result of which cracks may occuron the surface of the bush 5.

However, by doing as described above and by selecting an appropriateapical angle α, as well as a good rounding between the cone part 9 ofthe guide element 7 and the shaft part 2, the risk for said bush 5 todelaminate or of cracks being formed on the surface of the bush 5 willbe reduced to a minimum, if not eliminated, which again demonstrates thestrength of a method according to the invention.

Moreover, according to an alternative method of the invention which hasnot been discussed yet, it is not excluded to provide the bush with anumber of additional fibre-reinforced layers which merely serve as areinforcement during the mounting of the bush 5 on the shaft 1,precisely to prevent the aforesaid delaminating or cracks being formedin the bush 5 or cracks being formed on the surface of the bush 5 duringthe mounting.

As already postulated above, the bush 5 can for example be built of aninner layer, an intermediate layer, an axial layer and an outer layer,whereby after the bush 5 has been mounted on the shaft 1, one or severalof these layers can be removed again from the bush 5.

A major advantage of this method consists in that the layers of the bush5 which are preserved after it has been mounted can be made with alarger fibre density then if such temporarily reinforcing layers werenot applied.

In this way, the eventually mounted bush 5 may have a small thickness h,formed of one or several functional layers, but it can neverthelessexert a large radial pressure P on the shaft 1.

Another advantage of a method according to the invention is that theguide element 7, the shaft 1 and the press 13 can be very well alignedin a very simple manner, such that a failure mode, as shown in FIG. 17,can be avoided.

Due to a bad positioning of the guide element 7 in relation to the shaftpart 2, there will be a certain delamination of the layers of the bush 5and/or a buckle will be formed at the badly aligned transition betweenthe conical part 9 and the shaft part 2.

By providing the guide element 7 with a central passage 12 having aninner diameter D8 which corresponds to the diameter D2 of the shaft part3 adjacent to the part 2 of the shaft 1, as in the method according tothe invention, a good alignment is automatically obtained, as a resultof which a good alignment is self-evident and the aforesaid problems areavoided.

A good alternative for the composite bush 5 consists in making the bush5 of a preferably thin metal. A metal is hereby preferably selected witha yield point which is higher than the maximal tension occurring whilethe bush 5 is being mounted.

The invention is not restricted to the methods described up to now; onthe contrary, other analogous methods are not excluded either.

For example, another type of guide element 23 can be centred on theshaft in another manner, as is illustrated by means of FIG. 12.

In the given example of FIG. 12, the shaft 1 is provided with an inneropening 25 on its far end 24, whereas the guide element 23 is providedwith an axially protruding part 26 which is complementary to the inneropening 25 in the shaft 1.

In this way, it becomes possible to centre the guide element 23 on theshaft 1 by introducing it in the opening 25 of the shaft 1 with itsaxially protruding part 26.

This may be advantageous, for example, when a bush 5 must be fixed on apart 2 of the shaft 1 which is situated at or close to the far end 24 ofthe shaft 1.

According to yet another alternative method of the invention, it is notexcluded even to make the shaft 1 such that the guide element 7 is anintegral part of it, for example by providing the shaft 1 next to thepart 2 of the shaft 1 with a conical part over which the bush 5 can bepushed so as to obtain a radial expansion of the bush 5.

Also other methods whereby for example a press 13 is used in which oneor several telescopic accessories 17 and 22 are integrated are notexcluded either.

Also centring the different parts in relation to one another, such asthe guide element 7, the shaft 1, the accessories 17 and 22 and thepress 13, can be done in different ways.

Although in the figures, the part 2 of the shaft 1 on which the bush 5has to be mounted with a force fit is round/cylindrical, it is notexcluded for the invention to be applied on a part 2 of the shaft 1 withan oval/cylindrical shape or a cylindrical shape with key ways or thelike, or even on a part 2 of the shaft 1 with a conical shape.

The invention is by no means restricted to the methods and applicationsaccording to the invention described by way of example and representedin the accompanying drawings; on the contrary, such a method formounting a bush on a part of a shaft with a force fit can be realised inmany other ways or in other applications while still remaining withinthe scope of the invention.

1-21. (canceled)
 22. Method for mounting a bush around a part of a shaftwith a force fit, comprising the steps: providing a bush with differentlayers of composite, which are either or not fibre-reinforced, whereinthe layers which are located near an outer perimeter of the bush have agreater elasticity than the layers located near an inner wall of thebush; providing a guide element on the extension of said part of theshaft, said guide element having an outer surface which is at leastpartly conical and whose largest diameter deviates maximally fivepercent from the outer diameter of said part of the shaft; positioningthe guide element such that the largest diameter of the conical part isdirected to said part of the shaft; pushing the bush over the guideelement, on the side of the guide element with the smallest diameter,and to said part of the shaft; moving a press axially towards theconical part during a first step in sliding the bush over the guideelement, wherein the press is provided with a bearing face on which theentire end face of the bush rests during the pressing; and, using apress element with an inner diameter which is equal to or larger thanthe outer diameter of said part of the shaft during another step insliding the bush over the guide element.
 23. Method according to claim22, wherein, during the said first step to axially slide the bush overthe guide element, axially moving the press up to the conical part ofthe guide element.
 24. Method according to claim 22, wherein thesmallest diameter of the conical part is smaller than or just as largeas the inner diameter of the bush; and wherein, at least the guideelement of the bush has a rounding on the edge of the contact surfacebetween both.
 25. Method according to claim 24, wherein the radius ofthe rounding is located within a distance of 10⁻¹⁰ times the smallestdiameter of the conical part to 10⁻¹ times the smallest diameter of theconical part.
 26. Method according to claim 22, wherein the bush is madeof a plastic.
 27. Method according to claim 22, including making thebush of a fibre-reinforced composite with at least one of the followinglayers or a combination thereof: an inner layer whose fibres are woundin a direction extending between +/−70° and 90° in relation to theshaft; an intermediate layer whose fibres are wound in a directionextending according to a direction between +/−70° and 90° in relation tothe shaft; an axial layer whose fibres are wound in a directionextending according to a direction between 0 and +/−70° in relation tothe shaft; and, an outer layer whose fibres are wound in a directionextending between +/−70° and 90° in relation to the shaft.
 28. Methodaccording to claim 27, wherein the inner layer is made with carbonfibre.
 29. Method according to claim 28, wherein, in an additional step,the outer layer, the axial layer and/or the, intermediate layer arepartly or entirely removed after the bush has been applied over the partof the shaft.
 30. Method according to claim 22, wherein the apical angle(a) of the conical part of the guide element is selected to be smallerthan or as large as α, and wherein:α=k.|ε|.D4/(h.(D1-D4)) where: α=the maximal apical angle of the conicalpart in °; k=a factor which is selected on the basis of the way in whichthe bush is made and the material out of which the bush is made, whichfactor is within a range of 10⁻⁶ to 10⁻²; |ε|=the absolute value of themaximally possible elongation for the least elastic material componentof the bush or the plasticity limit of the metal of the shaft if theshaft is made of metal; h=the thickness of the wall of the bush in m;D4=the inner diameter of the bush in m; and D1=the outer diameter of thepart of the shaft in m.
 31. Method according to claim 30, wherein theguide element comprises a number of successive conical parts over itslongitudinal direction, wherein every conical part meets the formula ofclaim 30, whereby D1 is each time determined by the largest outerdiameter of the conical part.
 32. Method according to claim 22, whereinthe shaft is stepped and the guide element is at least partly hollow,including centering the guide element on the shaft by providing it withits hollow part over a shaft part with a smaller diameter than the partof the shaft over which the bush is to be received.
 33. Method accordingto claim 22, wherein the shaft is provided with a recess at a far endthereof and the guide element is provided with an axially protrudingpart which is complementary to the recess in the shaft, wherein theguide element is centred on the shaft by introducing it at least partlyin the recess of the shaft with its axially protruding part.
 34. Methodaccording to claim 22, wherein the outer surface of the guide element isprovided with a cylindrical part which connects to the conical part, onthe side of this conical part with the smallest diameter.
 35. Methodaccording to claim 34, wherein the outer diameter of the cylindricalpart of the guide element is smaller than or equal to the smallestdiameter of the conical part.
 36. Method according to claim 22, wherein,in order to push the bush over the guide element and on the part of theshaft, using a cylindrical press which is at least partly hollow. 37.Method according to claim 36, wherein the hollow press is provided witha recess having an inner diameter which corresponds practically to thediameter of the cylindrical part of the guide element, wherein thehollow press is moved over the cylindrical part of the guide elementduring the axial movement.
 38. Method according to claim 36, wherein thehollow press is provided with an overhang which rests against an endface of the bush during the first step to facilitate axially shiftingthe bush over the guide element.
 39. Method according to claim 38,wherein, in a following step, an accessory is first provided between thepress and the guide element, which accessory has a recess with an innerdiameter which is larger than the inner diameter of the bush.
 40. Methodaccording to claim 38, wherein several successive steps are used whenaxially sliding the bush over the guide element, wherein an accessorywith an ever increasing inner diameter is used in every subsequent step.41. Method according to claim 22, wherein the guide element is anintegral part of the shaft.
 42. Method according to claim 22, whereinthe part of the shaft on which the bush is to be mounted with a forcefit has a cylindrical shape.